Re: [PATCH v2 4/6] drm/tidss: Set bus_format correctly from bridge/connector

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

On 09/11/2020 19:05, Nikhil Devshatwar wrote:
> When there is a chain of bridges attached to the encoder,
> the bus_format should be ideally set from the input format of the
> first bridge in the chain.
> 
> Use the bridge state to get the negotiated bus_format.
> If the bridge does not support format negotiation, error out
> and fail.
> 
> Signed-off-by: Nikhil Devshatwar <nikhil.nd@ti.com>
> ---
>  drivers/gpu/drm/tidss/tidss_encoder.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_encoder.c b/drivers/gpu/drm/tidss/tidss_encoder.c
> index e278a9c89476..ba5b6fccabe7 100644
> --- a/drivers/gpu/drm/tidss/tidss_encoder.c
> +++ b/drivers/gpu/drm/tidss/tidss_encoder.c
> @@ -22,6 +22,7 @@ static int tidss_encoder_atomic_check(struct drm_encoder *encoder,
>  	struct drm_device *ddev = encoder->dev;
>  	struct tidss_crtc_state *tcrtc_state = to_tidss_crtc_state(crtc_state);
>  	struct drm_display_info *di = &conn_state->connector->display_info;
> +	struct drm_bridge_state *bstate;
>  	struct drm_bridge *bridge;
>  	bool bus_flags_set = false;
>  
> @@ -41,17 +42,22 @@ static int tidss_encoder_atomic_check(struct drm_encoder *encoder,
>  		break;
>  	}
>  
> -	if (!di->bus_formats || di->num_bus_formats == 0)  {
> -		dev_err(ddev->dev, "%s: No bus_formats in connected display\n",
> -			__func__);
> -		return -EINVAL;
> -	}
> -
> -	// XXX any cleaner way to set bus format and flags?
> -	tcrtc_state->bus_format = di->bus_formats[0];
>  	if (!bus_flags_set)
>  		tcrtc_state->bus_flags = di->bus_flags;
>  
> +	/* Copy the bus_format from the input_bus_format of first bridge */
> +	bridge = drm_bridge_chain_get_first_bridge(encoder);
> +	bstate = drm_atomic_get_new_bridge_state(crtc_state->state, bridge);
> +	if (bstate)
> +		tcrtc_state->bus_format = bstate->input_bus_cfg.format;
> +
> +	if (tcrtc_state->bus_format == 0 ||
> +	    tcrtc_state->bus_format == MEDIA_BUS_FMT_FIXED) {
> +
> +		dev_err(ddev->dev, "Bridge connected to the encoder did not specify media bus format\n");
> +		return -EINVAL;
> +	}
> +
>  	return 0;

We should also take the bus flags from the bridge state (next bridge's input_bus_cfg.flags).

And... If I read this right, we always fail if there's no bstate. So we could just do "if (!bstate)
fail;"

And if we always expect to have bstate, and get bus flags and formats from there, we don't need the
current drm_for_each_bridge_in_chain() loop or taking bus_flags from display info.

 Tomi

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